It is well known in the art to break glass by first scribing the surface with a sharp edged wheel made of a hard material such as tungsten carbide.
The tools which have been used for this purpose include wheels which are spring loaded in an attempt to provide a constant scribing force on the glass. An example of such a tool is disclosed in R. P. Detorre's U.S. Pat. No. 3,577,636. Tungsten carbide cutter wheels are disclosed, for example, in the Bier et al U.S. Pat. No. 3,756,104. The prior art also discloses mechanisms for reducing or controlling the interference between the sheet of glass and the cutting wheel at the point of entry of the wheel. Insolio's U.S. Pat. No. 3,276,302, for example, discloses the use of plastic wheels which serve to lift the cutter wheel in advance of actual entry onto the glass by the cutter wheel. In this way the interference dimension is controlled to a predetermined point. Absent this sort of control, the entry edge of the glass sheet will either be damaged by chipping or cracking or the scoring will not be of a proper depth at the glass edge to ultimately produce a clean fracture. Insolio's patent, supra, also teaches the use of dual plastic guide wheels for allowing scribing in either of two directions.
It is well known in the art that a scribed sheet of glass exhibits a healing characteristic which becomes more pronounced as time passes after the scribing operation. It is generally necessary to complete the glass cutting operation by fracturing within one-half hour of the scribing operation in order to produce reasonable quality in the fracture.